Personally, I prefer wall ovens (or at least, raised ovens). It's so much easier if you don't have to bend over to deal with what's in your oven! I don't know of any reason why it would be preferrable to have an under range oven if your space allows otherwise.

Best reason is that things break. And they will be beyond repair at different times. If your oven in a range can't be repaired, you have to replace the range even though the cooking surface may be fine and a second oven may be as well. Not much goes wrong with gas appliances but electric circuits wear out.My 20 year old convection oven broke last year. The difference between repair and replacement was $200. No brainer. The separate 20 year old gas cooktop is in perfect condition.

The combined cost of separate wall ovens and cooktops is comparable to or less than dual-fuel range which is the most common choice. You do have to purchase a specialty cabinet to accomodate the wall ovens and that does mean loss of some counterspace unless you mount an oven under-counter.Separate units also allow you to choose from two different manufacturers. You may covet the $2500 BlueStar cooktop and be perfectly happy with the $1500 GE Profile convection oven (or something even less expensive.) That's a lot less than the cost of the BlueStar range. Depends on how you cook.A separate cooktop allows space underneath for pot storage. It also keeps the heat of the oven away from the work area which is important if you live where it's really hot. Even if you can't stand the heat, you can't always get out of the kitchen.

When we did our new house I put in two wall ovens, not a double oven. Normally with the double ovens the lower one is smaller which I didn't want. The cost for two ovens was basically the same as a double oven. Plus, I was able to get larger overns, 29" or something in that area. And, both were self cleaning.

Couple of items to consider when looking at wall ovens that no sales person in the world will mention.

Exhaust vent. Find out if it vent from the top or the bottom. Mrs Jfood is 5'0" and when the wall ovens are on she gets a blast of air as she walks by, not a happy camper. Our old one vented from the bottom and only the dog knew about it. Exposed versus hidden coils. Major trade-off to consider. The hidden coil on the bottom makes it easier to clean but adds time to the pre-heat cycle. It takes me 20 minutes to 350 and over 30 minutes to 425-450. Something to consider if quick roasted chicken is a staple duringthe week.Convection - Think about three different convection settings, conv bake, conv roast, conv broil. Difference among the three is which element(s) come(s) on to cycle up the temperature.

Cooktop - your major decision will be the venting system. Up or down. We have the 36" viking with down. There are pluses and minus to this system versus an updraft.

Once you get a little further along, post and see if we can give some more defined guidance.